JP7354032B2 - Mask blank, transfer mask, and semiconductor device manufacturing method - Google Patents

Description

The present invention relates to a mask blank, a transfer mask manufactured using the mask blank, and a method for manufacturing a semiconductor device using the above-described transfer mask.

Generally, in the manufacturing process of semiconductor devices, fine patterns are formed using photolithography. Further, to form this fine pattern, usually a number of substrates called transfer masks are used. In order to miniaturize the pattern of a semiconductor device, in addition to miniaturizing the mask pattern formed on the transfer mask, it is necessary to shorten the wavelength of the exposure light source used in photolithography. In recent years, exposure light sources used in the manufacture of semiconductor devices have become shorter in wavelength, from KrF excimer lasers (wavelength: 248 nm) to ArF excimer lasers (wavelength: 193 nm).

In recent years, a phase shift mask called a halftone phase shift mask has been developed as one of these transfer masks. This halftone type phase shift mask has a mask pattern formed on a transparent substrate, with a part (light transmitting part) that transmits light with an intensity that substantially contributes to exposure, and a part (light transmitting part) with an intensity that does not substantially contribute to exposure. It consists of a part that transmits light (a light semi-transmissive part), and the phase of the light passing through the light semi-transmissive part is shifted so that the phase of the light that passes through the light semi-transmissive part is different from the light transmitting part. By creating a relationship that is substantially inverted with respect to the phase of the transmitted light, the contrast at the boundary is improved so that the light transmitted near the boundary between the light transmitting part and the light semi-transmitting part cancels each other out. It is designed to be able to maintain good retention.

However, as the wavelength of the laser beam used for exposure becomes shorter, the energy of the laser beam increases, and therefore the damage to the light semi-transparent film due to exposure increases. In order to increase the durability of the light semi-transparent film against laser light, it is effective to make the light semi-transparent film dense. However, on the other hand, if the sheet resistance of the light semi-transparent film becomes large, when patterning is performed using electron beam lithography on the resist film formed on it, charges accumulate in the light semi-transparent film and charge up. A problem occurred where the pattern could not be drawn.
In contrast, in Patent Document 1, an exposed portion 5 where the phase shift film 2 does not exist is formed at the peripheral portion of the transparent substrate 1, and the resist film 4 is conductive enough to prevent charge-up when patterning the resist film 4 by electron beam lithography. A technique is disclosed in which charge-up is suppressed by forming a light-shielding film made of a material having the following properties so as to cover the exposed portion 5 and the phase shift film 2.

Japanese Patent Application Publication No. 2006-184353

In the mask blank described above, the light shielding film is formed in a wide area covering the chamfered surface and side surfaces of the substrate. On the other hand, as patterns become finer, light-shielding films, which are also used as hard masks, are becoming thinner, with a thickness of 40 nm or less. Generally, a thin film including a light shielding film of a mask blank is formed on a substrate by a sputtering method. When forming a thin film by sputtering, the angle of incidence of sputtered particles on a chamfered surface or side surface is more acute than the angle of incidence of sputtered particles on the main surface of a substrate. For this reason, the thickness of the thin film formed on the chamfered surface or side surface is significantly thinner than the thickness of the thin film formed on the main surface. Further, the adhesion force of the thin film formed on the chamfered surface or side surface is weaker than the adhesion force of the thin film formed on the main surface. Due to these circumstances, there has been a problem in that the light shielding film formed on the chamfered surface or side surface of the substrate tends to peel off, and when the mask blank is handled, the light shielding film on those parts easily peels off and generates dust. To solve this problem, when forming a light-shielding film by sputtering, the outer edge of the film-forming region (thin film formation region) of the light-shielding film is located inside the ridgeline of the chamfered surface of the main surface of the substrate. Therefore, we attempted to control the ground pin so that it is located outside of the contact position when it is set in an electron beam lithography system.

Conventionally, when controlling the area of a thin film to be formed on the main surface of a substrate, sputtering is performed with a masking plate installed on the substrate to mask areas where the thin film is not desired to be formed. That is, sputtering is performed with only the area on the main surface of the substrate where a thin film is desired to be formed (hereinafter sometimes referred to as a "design area") exposed. By performing sputtering with this masking plate in contact with the main surface of the substrate, it is possible to avoid forming a thin film wrapping around the chamfered surface or side surface of the substrate. However, in that case, a problem arises in that the contact between the masking plate and the main surface of the substrate causes scratches and foreign matter on the substrate due to rubbing and friction. For this reason, sputtering is performed with the masking plate placed in a non-contact state with the main surface of the substrate. During sputtering, most of the sputtered particles are incident on the main surface of the substrate in a direction that is inclined to some extent from a direction perpendicular to the main surface of the substrate. Furthermore, floating sputtered particles also exist within the sputtering apparatus. For these reasons, it is inevitable that a certain amount of sputtered particles will enter and accumulate in the gap between the main surface of the substrate and the masking plate. In other words, after sputtering is completed, a desired thickness is formed in the designed area on the main surface of the substrate, but a thin film is also formed slightly outside the boundary of the designed area. Become.

In particular, when forming a highly conductive thin film such as a light-shielding film, it is required that the thin film be formed outside the position where an earth pin of an electron beam lithography device or the like comes into contact. The position where the ground pin makes contact is often a position close to the ridge line with the chamfered surface on the main surface of the substrate. If it is necessary to form such a thin film in an area close to the ridgeline of the chamfered surface on the main surface, if the positional accuracy when installing the masking plate is low, sputtered particles may adhere to the chamfered surface or side surfaces. Otherwise, a thin film may be formed. That is, in order to control the thin film formation region, it is necessary to improve the positional accuracy of the masking plate of the sputtering device.

As a method to check the positional accuracy of the masking plate, we actually set up the masking plate on the substrate, formed a light-shielding film by sputtering, and then visually checked the area where the light-shielding film was formed by magnifying it with an optical camera. Ta. As a result, it may be difficult to confirm the boundary between the area where the light shielding film is formed and the area where the light shielding film is not formed, which has been a problem. Further, such a problem is not limited to light shielding films, but may also occur in masks for other uses that include a thin film on a substrate.

The present invention was made to solve the conventional problems, and when a thin film is formed on a substrate, the area where the thin film is formed and the area where the thin film is not formed (area where the substrate is exposed) The purpose is to make it easy to visually recognize the boundaries between In addition, this makes it possible to easily adjust the position of the masking plate installed in the sputtering equipment that forms the thin film, so as to avoid forming the thin film by wrapping around the sides and chamfered surfaces of the substrate. is intended to provide. Furthermore, it is an object of the present invention to provide a transfer mask manufactured using this mask blank. An object of the present invention is to provide a method for manufacturing a semiconductor device using such a transfer mask.

In order to achieve the above object, the present invention has the following configuration.
(Configuration 1)
A mask blank comprising a substrate and a thin film,
The substrate has two main surfaces and a side surface, and a chamfered surface is provided between the two main surfaces and the side surface,
One of the two main surfaces has an inner region including the center of the main surface and an outer peripheral region outside the inner region,
the thin film is provided on an inner region of the main surface;
The surface reflectance Rs of the outer peripheral region of the main surface with respect to light with a wavelength of 400 nm to 700 nm is 10% or less,
When the surface reflectance for light with a wavelength of 400 nm to 700 nm at one of the locations where the film thickness of the thin film is within the range of 9 nm to 10 nm is Rf, the contrast ratio (Rf/Rs) is 3.0. A mask blank characterized by the above.

(Configuration 2)
The mask blank according to configuration 1, wherein the surface reflectance at the one location for light with a wavelength of 400 nm to 700 nm is 20% or more.
(Configuration 3)
When the surface reflectance for light with a wavelength of 400 nm at the one location is RfB, the surface reflectance for light with a wavelength of 550 nm at the one location is RfG, and the surface reflectance for light with a wavelength of 700 nm at the one location is RfR. , the standard deviation calculated between the three surface reflectances RfB, RfG, and RfR is 1.0 or less, the mask blank according to configuration 1 or 2.

(Configuration 4)
4. The mask blank according to any one of configurations 1 to 3, wherein the thin film has an extinction coefficient k of 1.5 or more for light having a wavelength of 400 nm to 700 nm.
(Configuration 5)
5. The mask blank according to any one of configurations 1 to 4, wherein the thin film has an average thickness of greater than 10 nm and less than or equal to 60 nm.

(Configuration 6)
Any one of configurations 1 to 5, wherein an intermediate film is provided between the main surface and the thin film in an inner region from the outer edge of the inner region toward the center of the one main surface. Mask blank as described in Crab.
(Configuration 7)
7. The mask blank according to configuration 6, wherein the intermediate film is a semi-transparent film that transmits exposure light from an ArF excimer laser with a transmittance of 1% or more.

(Configuration 8)
A transfer mask, characterized in that the thin film in the mask blank according to any one of Structures 1 to 5 is provided with a transfer pattern.
(Configuration 9)
8. A transfer mask according to configuration 6 or 7, wherein the intermediate film is provided with a transfer pattern, and the thin film is provided with a pattern including a light-shielding band.

(Configuration 10)
A method for manufacturing a semiconductor device, comprising the step of exposing and transferring a transfer pattern to a resist film on a semiconductor substrate using the transfer mask according to Structure 8 or 9.

According to the mask blank of the present invention, when a thin film is formed on a substrate, it becomes easy to visually recognize the boundary between the region where the thin film is formed and the region where the thin film is not formed. Thereby, it is possible to easily adjust the position of the masking plate provided in the sputtering apparatus for forming a thin film so as to avoid forming the masking plate around the side surface or chamfered surface of the substrate.

FIG. 1 is a cross-sectional view of main parts showing the configuration of a mask blank in an embodiment of the present invention. FIG. 1 is a schematic plan view of a substrate in an embodiment of the present invention. FIG. 3 is a schematic cross-sectional view showing a manufacturing process of a phase shift mask in an embodiment of the present invention. FIG. 2 is a schematic diagram of main parts of a masking plate used when forming a thin film of a mask blank in an embodiment of the present invention. 3 is a graph showing a film thickness profile near the boundary between the main surface and the light shielding film according to Example 1. FIG.

Hereinafter, before describing embodiments of the present invention, the circumstances leading to the present invention will be described.
The present inventors have discovered that when a thin film is formed on a substrate, it is easy to visually recognize the boundary between the region where the thin film is formed and the region where the thin film is not formed (the region where the substrate is exposed). As a result, we are working diligently to develop a mask blank configuration that can easily adjust the position of the masking plate installed in the sputtering equipment that forms thin films, so as to avoid forming the masking plate around the sides and chamfered surfaces of the substrate. conducted research.

Due to the above-mentioned circumstances, even if a thin film is formed by sputtering using a masking plate, it is inevitable that a certain amount of sputtered particles will enter the gap between the main surface of the substrate and the masking plate and be deposited. That is, a desired thickness is formed in the design area on the main surface of the substrate, but a thin film is also formed slightly outside the boundary of the design area, albeit with a smaller thickness. The formed thin film has a substantially uniform thickness in the region of the main surface not covered by the masking plate. However, due to the influence of sputtered particles entering the gap between the masking plate and the main surface of the substrate, the ends of the thin film do not have vertical sidewalls. In other words, the edge of the thin film is a certain distance outside the design area of the main surface, and the thickness of the thin film formed outside the design area increases from the boundary of the design area to the edge. It has a shape that becomes thinner.

It is inevitable that the distance from the boundary of the design area on the main surface to the end of the thin film will be different even between two sputtering apparatuses having the same design specifications. Even when the same sputtering equipment is used, differences occur depending on the sputtering conditions. For this reason, a thin film is actually formed on the substrate on which the masking plate is installed under the designed film forming conditions, and the position of the edge of the thin film is checked to adjust the position of the masking plate. The present inventors took into consideration the relatively high frequency of adjusting the position of the masking plate, and developed a method (hereinafter referred to as "this method") that uses image data captured by an imaging camera such as a CCD to identify the edge of a thin film. (Sometimes referred to as "image recognition method."). When using this image identification method, it is difficult to accurately detect the boundary between a region where a thin film is formed on the main surface and a region where it is not formed (a region where the main surface is exposed). In this image identification method, areas where a contrast ratio of more than a certain level is obtained between the light reflected in an area where a thin film is not formed and the light reflected in an area where a thin film is formed are identified by a thin film. identified as existing. The position of the outermost edge of the area where the thin film identified by this image identification method exists is slightly inside the position of the outermost edge of the area where the thin film actually exists.

As a result of intensive research by the present inventors, we have found that depending on the structure of the thin film, the outermost position of the area where the thin film is identified by the image recognition method and the outermost position of the area where the thin film actually exists may differ. It has been found that the difference from the position of the outer end becomes large, and the accuracy of position adjustment of the masking plate may become low. Therefore, the present inventors investigated the tendency of the thickness of the thin film formed by sputtering on the main surface of the substrate from the design area to the edge of the thin film, and determined the thickness of the thin film and the visible light ( Specifically, we focused on the relationship between the reflectance of light with a wavelength of 400 nm to 700 nm (hereinafter, light in this wavelength range may be referred to as "light in the visible light range"), and conducted further intensive studies.

First, based on the tendency of the thickness of the thin film, if the presence of the thin film can be identified at a point where the thickness of the thin film is at most 10 nm using the image acquisition method described above, then the outermost edge of the area where the thin film actually exists It was found that the difference between the position of In order to easily identify the presence of a thin film at that location on the thin film, it is desirable that the surface reflectance for light in the visible light range be low in the outer peripheral region of the main surface of the substrate where the thin film is not formed. It has been found that the surface reflectance is preferably 10% or less. On top of that, in order to be able to identify the presence of a thin film at that location, it is necessary to determine the surface reflectance of the thin film at that location for light in the visible light range and the location where the main surface of the substrate is exposed. It has been found that it is desirable that the contrast ratio between the surface reflectance and the visible light range is 3.0 or more. Furthermore, it has been found that in order to easily identify the presence of a thin film, it is desirable to maintain the contrast ratio above 3.0 even if the thickness of the thin film is reduced from 10 nm to 1 nm.

That is, the mask blank of the present invention is a mask blank comprising a substrate and a thin film, the substrate having two main surfaces and a side surface, and a chamfered surface between the two main surfaces and the side surface. one of the two main surfaces has an inner region including the center of the main surface and a peripheral region outside the inner region, and the thin film is disposed on the inner region of the main surface. is provided, the surface reflectance Rs of the outer peripheral region of the main surface for light with a wavelength of 400 nm to 700 nm is 10% or less, and the thickness of the thin film is in one of the locations within the range of 9 nm to 10 nm. It is characterized in that the contrast ratio (Rf/Rs) is 3.0 or more, where Rf is the surface reflectance for light with a wavelength of 400 nm to 700 nm.

FIG. 1 is a cross-sectional view showing the configuration of a mask blank 100 according to an embodiment of the present invention. A mask blank 100 of the present invention shown in FIG. 1 has a structure in which a phase shift film 20, a light shielding film 30, and a hard mask film 31 are laminated in this order on a transparent substrate 10.

The light-transmitting substrate 10 can be formed of quartz glass, aluminosilicate glass, soda lime glass, low thermal expansion glass (SiO ₂ --TiO ₂ glass, etc.) in addition to synthetic quartz glass. Among these, synthetic quartz glass is particularly preferable as a material for forming the transparent substrate of the mask blank because it has high transmittance to ArF exposure light and sufficient rigidity to prevent deformation. The substrate 10 accommodated in a chamber (not shown) has two main surfaces 11 (11a, 11b), a side surface 12, and a chamfer formed by chamfering the boundary between the main surface 11 and the side surface 12. It has a surface 13. The boundary between the main surface 11 and the chamfered surface 13 is preferably less than 0.5 mm from the side surface 12 of the substrate, more preferably 0.4 mm or less, when viewed from the main surface 11 side.

As shown in FIG. 2, one of the two main surfaces 11, 11a, has an inner region 14 including the center 17 of the main surface 11a, and an outer peripheral region 15 outside the inner region 14. . A thin light-shielding film 30 is provided on this inner region 14 . The light shielding film 30 is not substantially formed in the outer peripheral region 15, that is, the main surface 11a is substantially exposed. In a state in which the light shielding film 30 is not substantially formed or in a state in which the main surface 11a is substantially exposed, sputtered particles constituting the light shielding film 30 are slightly attached and deposited to a thickness of less than 1 nm. It also includes the state. This level of deposition is unlikely to cause defects, and there is no substantial difference between the surface reflectance Rs and the state in which the main surface 11a is completely exposed. Note that the boundary line and center 17 between the inner region 14 and the outer peripheral region 15 shown in FIG. 2 are virtual ones added for explanation, and are not necessarily actually attached on an actual board. I would like to add this point just in case.

The boundary line between the inner region 14 and the outer peripheral region 15 is preferably 0.05 mm or more inward from the boundary between the chamfered surface 13 and the main surface 11a of the substrate 10.
Further, the surface reflectance Rs of the outer peripheral region 15 of the substrate 10 for light having a wavelength of 400 nm to 700 nm is preferably 10% or less, more preferably 8% or less, and still more preferably 7% or less. preferable. Both the surface reflectance Rs and the surface reflectance Rf, which will be described later, can be measured based on image data taken with an imaging camera such as a CCD. By setting the surface reflectance Rs of the outer peripheral region 15 in the above range, the surface reflectance Rf of the thin film for light with a wavelength of 400 nm to 700 nm when the film thickness of the thin film is within the range of 9 nm to 10 nm. It becomes easier to adjust the contrast ratio to 3.0 or more.

In this embodiment, as shown in FIG. 1, in the inner region from the boundary between the inner region 14 and the outer peripheral region 15 toward the center 17 side of the main surface 11a, the main surface 11a and the light shielding film 30, which is a thin film, are connected to the main surface 11a. A phase shift film 20, which is an intermediate film, is provided between the two.
The phase shift film 20 is made of a material containing silicon.
The phase shift film 20 has a function (transmittance) of transmitting the exposure light of the ArF excimer laser with a transmittance of 1% or more, and a thickness that is the same as that of the phase shift film 20 for the exposure light transmitted through the phase shift film 20. It is preferable that it is a light semi-transparent film that has a function of creating a phase difference of 150 degrees or more and 210 degrees or less with the exposure light that has passed through the air by a certain distance. Further, the transmittance of the phase shift film 20 is preferably 1% or more, and more preferably 2% or more. The transmittance of the phase shift film 20 is preferably 30% or less, more preferably 20% or less.

The thickness of the phase shift film 20 is preferably 80 nm or less, more preferably 70 nm or less. The thickness of the phase shift film 20 is preferably 50 nm or more. This is because a thickness of 50 nm or more is required in order to form the phase shift film 20 with an amorphous material and make the phase difference of the phase shift film 20 150 degrees or more.

In the phase shift film 20, in order to satisfy the various conditions related to the optical properties and film thickness, the refractive index n of the phase shift film with respect to exposure light (ArF exposure light) is preferably 1.9 or more, and 2 More preferably, it is .0 or more. Further, the refractive index n of the phase shift film 20 is preferably 3.1 or less, more preferably 2.7 or less. The extinction coefficient k of the phase shift film 20 for ArF exposure light is preferably 0.26 or more, and more preferably 0.29 or more. Further, the extinction coefficient k of the phase shift film 20 is preferably 0.62 or less, more preferably 0.54 or less.

Note that the refractive index n and extinction coefficient k of the thin film including the phase shift film 20 are not determined only by the composition of the thin film. The film density and crystal state of the thin film are also factors that influence the refractive index n and extinction coefficient k. For this reason, various conditions for forming a thin film by reactive sputtering are adjusted so that the thin film has a desired refractive index n and extinction coefficient k. In order to make the phase shift film 20 have a refractive index n and an extinction coefficient k in the above range, when forming it by reactive sputtering, a mixed gas of a noble gas and a reactive gas (oxygen gas, nitrogen gas, etc.) is used. Although it is effective to adjust the ratio, it is not limited thereto. There are various factors such as the pressure inside the film forming chamber during formation by reactive sputtering, the electric power applied to the sputter target, and the positional relationship such as the distance between the target and the transparent substrate 10. Further, these film forming conditions are specific to the film forming apparatus, and are appropriately adjusted so that the formed phase shift film 20 has a desired refractive index n and extinction coefficient k.

The mask blank 100 includes a thin light shielding film 30 on the phase shift film 20 . Generally, in a binary transfer mask, the outer peripheral area of the area where the transferred pattern is formed (transfer pattern forming area) is exposed to light that is transmitted through the outer peripheral area when transferred to the resist film on the semiconductor wafer using an exposure device. In order to prevent a resist film from being affected by exposure light, it is required to ensure an optical density (OD) of a predetermined value or higher. Regarding this point, the same applies to the phase shift mask. Normally, it is desirable that the outer peripheral region of a transfer mask including a phase shift mask has an OD of 3.0 or more, and is required to have an OD of at least 2.0. The phase shift film 20 has a function of transmitting exposure light with a predetermined transmittance, and it is difficult to ensure a predetermined optical density using only the phase shift film 20. Therefore, at the stage of manufacturing the mask blank 100, it is necessary to stack the light shielding film 30 on the phase shift film 20 in order to ensure the insufficient optical density. With such a structure of the mask blank 100, the light shielding film 30 in the area where the phase shift effect is used (basically the transfer pattern forming area) can be removed during the manufacturing of the phase shift mask 200 (see FIG. 3). By doing so, it is possible to manufacture the phase shift mask 200 in which the optical density of the predetermined value is ensured in the outer peripheral region.

Further, the light shielding film 30 needs to function as an etching mask during dry etching using a fluorine gas to form a transfer pattern (phase shift pattern) on the phase shift film 20. Therefore, it is necessary to use a material for the light shielding film 30 that has sufficient etching selectivity with respect to the phase shift film 20 in dry etching using a fluorine-based gas. The light shielding film 30 is required to be able to accurately form the fine pattern to be formed on the phase shift film 20. The average thickness of the light shielding film 30 is preferably 60 nm or less, more preferably 50 nm or less, and even more preferably 40 nm or less. If the film thickness of the light shielding film 30 is too thick, the fine pattern to be formed cannot be formed with high precision. On the other hand, the light shielding film 30 is required to satisfy the required optical density as described above. Therefore, the average thickness of the light-shielding film 30 is required to be greater than 10 nm, and preferably 15 nm or more, excluding the end region that forms the boundary between the inner region 14 and the outer peripheral region 15. Here, the average film thickness is not particularly limited, but the region where the light shielding film 30 is formed is divided into areas of approximately 55 μm x approximately 55 μm, and the average film thickness measured in each area is calculated as follows: It can be calculated by taking

In this embodiment, the light shielding film 30, which is a thin film, has a surface reflectance Rf for light having a wavelength of 400 nm to 700 nm at one of the locations where the film thickness of the light shielding film 30 is within the range of 9 nm to 10 nm. When this happens, the contrast ratio (Rf/Rs) is configured to be 3.0 or more. This makes it easy to identify the boundary between the region where the light shielding film 30, which is a thin film, is formed and the region where it is not formed. Moreover, from the viewpoint of visibility, it is preferable that the surface reflectance Rf at the one location is 20% or more for light with a wavelength of 400 nm to 700 nm.

As described above, the location of the light shielding film 30 (thin film) that determines the above-mentioned surface reflectance Rf is not strictly speaking the outermost end of the light shielding film 30. However, the difference between the position of that part of the light shielding film 30 and the position of the outermost end is small, and it is sufficiently possible to adjust the position of the masking plate based on this difference.
From the viewpoint of ensuring conductivity, the sheet resistance value of the light shielding film 30 is preferably 1 kΩ/square or less, more preferably 0.5 kΩ/square or less.

The light shielding film 30 has a surface reflectance of RfB for light with a wavelength of 400 nm at one of the locations where the film thickness is within the range of 9 nm to 10 nm, and a surface reflectance of RfG for light with a wavelength of 550 nm at the above one location. , when the surface reflectance for light with a wavelength of 700 nm at the one location is RfR, the standard deviation calculated between the three surface reflectances RfB, RfG, and RfR is preferably 1.0 or less. . It can be obtained relatively easily from the RGB values of image data taken with an imaging camera such as a CCD. The presence of the light shielding film 30 is easier to visually recognize when the deviation of each reflectance for light of the three wavelengths is smaller.

From the viewpoint of visibility, the extinction coefficient k of the light shielding film 30 for light having a wavelength of 400 nm to 700 nm is preferably 1.5 or more, and more preferably 2.0 or more. Further, the extinction coefficient k of the light shielding film 30 for the above light is preferably 4.0 or less, more preferably 3.5 or less.
The light shielding film 30 can have either a single layer structure or a laminated structure of two or more layers. In addition, even if each layer of a single-layer light-shielding film and a light-shielding film with a laminated structure of two or more layers has a composition that is almost the same in the thickness direction of the film or layer, the composition may be graded in the thickness direction of the layer. It may be a configuration.

The light shielding film 30 may be formed of any material as long as it satisfies the contrast ratio conditions described above. The light shielding film 30 is preferably formed of a material containing chromium. The chromium-containing material forming the light shielding film 30 may be selected from chromium metal, chromium (Cr), oxygen (O), nitrogen (N), carbon (C), boron (B), and fluorine (F). Examples include materials containing one or more elements. Generally, chromium-based materials are etched with a mixed gas of chlorine-based gas and oxygen gas, but the etching rate of chromium metal with this etching gas is not very high. Considering that the etching rate of the mixed gas of chlorine-based gas and oxygen gas is increased, the material for forming the light-shielding film 30 is chromium and one or more elements selected from oxygen, nitrogen, carbon, boron, and fluorine. A material containing is preferred. Further, the chromium-containing material forming the light shielding film 30 may contain one or more elements among molybdenum, indium, and tin. By containing one or more elements among molybdenum, indium, and tin, the etching rate for a mixed gas of chlorine-based gas and oxygen gas can be made faster.

The light shielding film 30 can be formed on the phase shift film 20 by a reactive sputtering method using a target containing chromium. The sputtering method may be one using a direct current (DC) power source (DC sputtering) or one using a radio frequency (RF) power source (RF sputtering). Further, a magnetron sputtering method or a conventional method may be used. DC sputtering is preferable because its mechanism is simple. Further, it is preferable to use a magnetron sputtering method because the film formation rate becomes faster and productivity is improved. Note that the film forming apparatus may be of an in-line type or a single-wafer type.

The sputtering gases used when forming the light shielding film 30 include gases that do not contain oxygen and contain carbon (CH ₄ , C ₂ H ₄ , C ₂ H ₆ , etc.) and gases that do not contain carbon and contain oxygen (O ₂ , O ₃ , etc.) and a noble gas (Ar, Kr, Xe, He, Ne, etc.); a mixed gas containing a gas containing carbon and oxygen (CO ₂ , CO, etc.) and a noble gas; A mixed gas containing at least one of a gas, a gas containing carbon and oxygen, and a gas containing carbon but not oxygen (CH ₄ , C ₂ H ₄ , C ₂ H _6, etc.) and a gas containing oxygen but not containing carbon. Any one of them is preferred. In particular, it is safe to use a mixed gas of CO ₂ and noble gas as the sputtering gas, and since CO ₂ gas has lower reactivity than oxygen gas, the gas can circulate uniformly over a wide range within the chamber. This is preferable because the quality of the formed light shielding film 30 becomes uniform. The gases may be introduced into the chamber separately, or several gases may be introduced at once or all gases may be mixed.

The material of the target may be not only chromium alone but also chromium as a main component, and chromium containing either oxygen or carbon, or a target in which a combination of oxygen and carbon is added to chromium may be used.

Note that the mask blank of the present invention is not limited to that shown in FIG. Good too. In this case, it is preferable to form the etching stopper film with the above-mentioned chromium-containing material, and to form the light-shielding film 30 with a silicon-containing material or a tantalum-containing material.
Further, the mask blank of the present invention is not limited to the above-mentioned mask blank for a phase shift mask, but can also be applied to a mask blank for a binary mask. The mask blank in this case has a configuration in which the phase shift film 20 is not provided between the main surface 11a of the transparent substrate 10 and the light shielding film 30. Further, the above-mentioned predetermined optical density is ensured only by the light shielding film 30. By forming a transfer pattern on the light shielding film 30 of such a mask blank, a binary mask (transfer mask) can be formed.
Further, the mask blank of the present invention may be a reflective mask blank for EUV lithography (Extreme Ultraviolet Lithography). In this case, it is preferable that the absorber film is made of the thin film of this embodiment.

The silicon-containing material that forms the light shielding film 30 may contain a transition metal or a metal element other than the transition metal. The pattern formed on the light-shielding film 30 is basically a light-shielding band pattern in the outer circumferential area, and the integrated irradiation amount of ArF exposure light is smaller than that in the transfer pattern area, and fine patterns are arranged in this outer circumferential area. This is because it is rare that ArF light resistance is low, and substantial problems are unlikely to occur even if the ArF light resistance is low. Further, when the light shielding film 30 contains a transition metal, the light shielding performance is greatly improved compared to the case where the transition metal is not contained, and the thickness of the light shielding film 30 can be made thinner. The transition metals contained in the light shielding film 30 include molybdenum (Mo), tantalum (Ta), tungsten (W), titanium (Ti), chromium (Cr), hafnium (Hf), nickel (Ni), and vanadium (V). , zirconium (Zr), ruthenium (Ru), rhodium (Rh), niobium (Nb), palladium (Pd), or an alloy of these metals.

In the mask blank 100, a hard mask film 31 made of a material having etching selectivity with respect to the etching gas used when etching the light shielding film 30 may be further laminated on the light shielding film 30. As shown in FIG. 1, since the hard mask film 31 is formed in a region inside the light shielding film 30, there is no problem in ensuring conductivity between the light shielding film 30 and the resist film. The hard mask film 31 only needs to be thick enough to function as an etching mask until the dry etching for forming a pattern on the light shielding film 30 immediately below it is completed, and basically the optical density is Not subject to any restrictions. Therefore, the thickness of the hard mask film 31 can be made significantly thinner than the thickness of the light shielding film 30. The resist film made of organic material only needs to be thick enough to function as an etching mask until the end of the dry etching process that forms the pattern on this hard mask film, so it can be used much more easily than before. The thickness can be reduced. Making the resist film thinner is effective in improving resist resolution and preventing pattern collapse, and is extremely important in meeting the demands for miniaturization.

When the light shielding film 30 is formed of a material containing chromium, this hard mask film 31 is preferably formed of the above-mentioned material containing silicon. In addition, since the hard mask film 31 in this case tends to have low adhesion to the resist film made of organic material, the surface of the hard mask film 31 is subjected to HMDS (Hexamethyldisilazane) treatment to improve the surface adhesion. It is preferable. Note that the hard mask film in this case is more preferably formed of SiO ₂ , SiN, SiON, or the like.

Further, in addition to the above-mentioned materials, a material containing tantalum can be used as the material of the hard mask film 31 when the light shielding film 30 is formed of a material containing chromium. Materials containing tantalum in this case include tantalum metal, as well as materials in which tantalum contains one or more elements selected from nitrogen, oxygen, boron, carbon, and silicon. For example, Ta, TaN, TaO, TaON, TaBN, TaBO, TaBON, TaCN, TaCO, TaCON, TaBCN, TaBOCN, TaSi, TaSiN, TaSiO, TaSiON, TaSiBN, TaSiBO, TaSiBON, TaSiC, TaSiCN, TaSiCO, TaSiCON, etc. It will be done. Further, when the light shielding film 30 is formed of a material containing silicon, the hard mask film 31 is preferably formed of the above-mentioned material containing chromium.

In the mask blank 100, a resist film of an organic material may be formed in contact with the surface of the light shielding film 30 (or the surface of the hard mask film 31 if the hard mask film 31 is formed). In the case of a fine pattern corresponding to the DRAM hp32 nm generation, the light shielding pattern to be formed on the light shielding film 30 may be provided with an SRAF (Sub-Resolution Assist Feature) with a line width of 40 nm. However, even in this case, by providing the hard mask film 31 as described above, the thickness of the resist film can be suppressed, and thereby the cross-sectional aspect ratio of the resist pattern made of this resist film can be reduced to 1:2.5. and can be lowered. Therefore, it is possible to prevent the resist pattern from collapsing or coming off during development, rinsing, etc. of the resist film. Note that the thickness of the resist film is more preferably 80 nm or less. The resist film is preferably a resist for electron beam exposure, and more preferably a chemically amplified resist.

The mask blank 100 having the above configuration is manufactured by the following procedure. First, a transparent substrate 10 is prepared. In this light-transmitting substrate 10, the side surfaces 12 and the main surface 11 are polished to a predetermined surface roughness (for example, the root mean square roughness Rq is 0.2 nm or less within the inner region of a rectangle with a side of 1 μm), and then , which has been subjected to predetermined cleaning and drying treatments.

Next, a phase shift film 20 is formed on this transparent substrate 10 by a sputtering method. After forming the phase shift film 20, an annealing treatment is performed at a predetermined heating temperature. Next, the above-mentioned light shielding film 30 is formed on the phase shift film 20 by a sputtering method.

FIG. 4 shows the main parts of the masking plate used when forming the light shielding film 30. As shown in the figure, both ends of the substrate 10 are positioned and held by substrate holders 51. A shielding plate 52 is provided above the substrate 10 to cover the peripheral edge thereof. The shielding plate 52 is provided in such a manner that its position can be adjusted so that it approaches or separates from the center 17 of the main surface 11a of the substrate 10 while maintaining a non-contact state with the substrate 10. By adjusting the positions of these shielding plates 52, it is possible to prevent the light shielding film material supplied from the sputtering target 50 from adhering to the peripheral edge of the substrate 10.

Then, the hard mask film 31 described above is formed on the light shielding film 30 by a sputtering method. In forming each layer by the sputtering method, a sputtering target and a sputtering gas containing the materials constituting each layer at a predetermined composition ratio are used, and if necessary, a mixed gas of the above-mentioned noble gas and reactive gas is added to the sputtering gas. Perform the formation using as. Thereafter, if this mask blank 100 has a resist film, HMDS (Hexamethyldisilazane) treatment is performed on the surface of the hard mask film 31 as necessary. Then, a resist film is formed on the surface of the HMDS-treated hard mask film 31 by a coating method such as a spin coating method, thereby completing the mask blank 100.

In the phase shift mask 200, which is a transfer mask of this embodiment, a transfer pattern (phase shift pattern) 20a is formed on the phase shift film 20 of the mask blank 100, and a light shielding pattern 30b including a light shielding band is formed on the light shielding film 30. It is characterized by In the case of a configuration in which the mask blank 100 is provided with a hard mask film, the hard mask film 31 is removed during the creation of the phase shift mask 200.

A method for manufacturing a phase shift mask 200 according to the present invention uses the mask blank 100 described above, and includes a step of forming a transfer pattern on the light shielding film 30 by dry etching, and using the light shielding film 30 having the transferred pattern as a mask. A step of forming a transfer pattern on the phase shift film 20 by dry etching, and a step of forming a light shielding pattern 30b on the light shielding film 30 by dry etching using a resist film having a light shielding band pattern (resist pattern 40b) as a mask. It is characterized by Hereinafter, a method for manufacturing the phase shift mask 200 of the present invention will be explained according to the manufacturing process shown in FIG.

First, a resist film is formed on the hard mask film 31 of the mask blank 100 by spin coating. Next, a first pattern (phase shift pattern) to be formed on the phase shift film 20 is exposed and drawn on the resist film using an electron beam. At this time, an earth pin (not shown) is in contact with the light shielding film 30 on which the resist film is formed, and grounding is ensured between the resist film and the light shielding film 30 (earth pin grounding point 16 in FIG. 2). ). Thereby, charge-up during exposure drawing can be suppressed. Thereafter, the resist film is subjected to predetermined processing such as PEB processing, development processing, and post-bake processing to form a first resist pattern 40a corresponding to the phase shift pattern on the resist film (see FIG. 3(a)). .

Next, using the resist pattern 40a as a mask, dry etching is performed on the hard mask film 31 using fluorine-based gas to form a hard mask pattern 31a, which is a first pattern, on the hard mask film 31 (FIG. 3(b)). reference). After this, the resist pattern 40a is removed. Here, the light shielding film 30 may be dry etched while the resist pattern 40a remains without being removed. In this case, the resist pattern 40a disappears during dry etching of the light shielding film 30.

Next, using the hard mask pattern 31a as a mask, dry etching is performed using an oxygen-containing chlorine gas to form a first pattern, a light-shielding pattern 30a, on the light-shielding film 30 (see FIG. 3C). The mixing ratio of the mixed gas of chlorine gas and oxygen gas in the dry etching of the light shielding film 30 is preferably chlorine gas: oxygen gas = 10 or more: 1 in the gas flow rate ratio in the etching apparatus. More preferably: 1 or more, and more preferably 20 or more: 1. By using an etching gas with a high mixing ratio of chlorine-based gas, the anisotropy of dry etching can be enhanced. In addition, in the dry etching of the light shielding film 30 , the mixing ratio of the mixed gas of chlorine-based gas and oxygen gas should be chlorine-based gas:oxygen gas = 40:1 or less as a gas flow rate ratio in the etching chamber. is preferred.

Next, using the light-shielding pattern 30a as a mask, dry etching is performed using fluorine-based gas to form a first pattern, the phase shift pattern 20a, on the phase shift film 20, and to remove the hard mask pattern 31a (see FIG. 3(d)). Next, a resist film is formed on the light shielding pattern 30a by spin coating. A light-shielding pattern, which is a second pattern to be formed on the light-shielding film 30, is exposed and drawn on the resist film using an electron beam. Thereafter, a predetermined process such as a development process is performed to form a resist film having a resist pattern 40b, which is a second pattern corresponding to the light-shielding pattern (see FIG. 3(e)).

Next, using the resist pattern 40b as a mask, dry etching is performed using a mixed gas of chlorine-based gas and oxygen gas to form a second pattern, the light-shielding pattern 30b, on the light-shielding film 30 (see FIG. 3(f)). ). Furthermore, the resist pattern 40b is removed and a predetermined process such as cleaning is performed to obtain the phase shift mask 200 (see FIG. 3(g)).

Note that there is no particular restriction on the chlorine-based gas used in the dry etching in the above manufacturing process as long as it contains Cl. For example, examples of the chlorine gas include Cl ₂ , SiCl ₂ , CHCl ₃ , CH ₂ Cl ₂ , CCl ₄ , and BCl ₃ . Further, there is no particular restriction on the fluorine-based gas used in the dry etching in the above manufacturing process as long as it contains F. For example, examples of the fluorine gas include CHF ₃ , CF ₄ , C ₂ F ₆ , C ₄ F ₈ , SF ₆ and the like. In particular, since a fluorine-based gas that does not contain C has a relatively low etching rate on a glass substrate, damage to the glass substrate can be further reduced.

The phase shift mask 200 of the present invention is manufactured using the mask blank 100 described above. Therefore, grounding to the resist can be ensured, and dust generation can be suppressed, so that good pattern transfer can be performed.

The method for manufacturing a semiconductor device of the present invention includes a step of exposing and transferring a transfer pattern to a resist film on a semiconductor substrate using the phase shift mask 200 or the phase shift mask 200 manufactured using the mask blank 100. It is characterized by being prepared. For this purpose, this phase shift mask 200 is set in an exposure device, and ArF exposure light is irradiated from the transparent substrate 1 side of the phase shift mask 200 to expose and transfer the transfer target (resist film on a semiconductor wafer, etc.). Even if this is done, the desired pattern can be transferred to the transfer target with high accuracy.

Hereinafter, embodiments of the present invention will be described in more detail with reference to Examples.
(Example 1)
[Manufacture of mask blank]
Referring to FIG. 1, a light-transmitting substrate 1 made of synthetic silica glass and having main surface dimensions of approximately 152 mm x approximately 152 mm and a thickness of approximately 6.35 mm was prepared. The main surface of the light-transmitting substrate 10 is polished to a predetermined surface roughness (Rq of 0.2 nm or less), and then subjected to a predetermined cleaning process and drying process. This transparent substrate 10 has two main surfaces 11 and four side surfaces 12, and has a chamfered surface 13 between the main surface 11 and the side surfaces 12. The boundary (edge line) between the chamfered surface 13 and the main surface 11 is located 0.4 mm from the side surface 12 of the substrate on the center 17 side when viewed from the main surface 11 side. When the surface reflectance Rs for light with a wavelength of 400 nm to 700 nm was measured at multiple locations on the main surface 11a of the transparent substrate 10, it was found that in all regions it was 7% or less (wavelength 400 nm: 6.99%, wavelength 550 nm: 6.75%, wavelength 700 nm: 6.62%).

Next, the transparent substrate 10 is installed in a single-wafer type DC sputtering apparatus, and a mixed sintered target of molybdenum (Mo) and silicon (Si) (Mo:Si=11 at%:89 at%) is used. By reactive sputtering (DC sputtering) using a mixed gas of argon (Ar), nitrogen (N ₂ ), and helium (He) as a sputtering gas, a phase shift film made of molybdenum, silicon, and nitrogen is deposited on the transparent substrate 10. Film 20 was formed with a thickness of 69 nm. During sputtering to form this phase shift film 20, a masking plate as shown in FIG. 4 was used. The masking plate used had a square opening with a side of 146 mm based on the center of the substrate.

Next, the transparent substrate 10 on which the phase shift film 20 was formed was subjected to heat treatment in order to reduce the film stress of the phase shift film 20 and to form an oxide layer on the surface layer. Specifically, heat treatment was performed using a heating furnace (electric furnace) in the atmosphere at a heating temperature of 450° C. and a heating time of 1 hour. When the transmittance and phase difference of the phase shift film 20 after the heat treatment for light with a wavelength of 193 nm were measured using a phase shift measurement device (MPM193 manufactured by Lasertec), the transmittance was 6.0% and the phase difference was 6.0%. It was 177.0 degrees (deg).

Next, the light-transmitting substrate 10 on which the phase shift film 20 is formed is placed in a single-wafer type DC sputtering apparatus, and using a chromium (Cr) target, argon (Ar), carbon dioxide (CO ₂ ), and helium Reactive sputtering (DC sputtering) was performed in a mixed gas atmosphere of (He). As a result, a light shielding film (CrOC film) 30 made of chromium, oxygen, and carbon was formed with a thickness of 18 nm in contact with the phase shift film 20. A masking plate was also used during sputtering to form this light shielding film 30. However, the masking plate used here has a square opening with one side of 150 mm based on the center of the substrate (that is, the design area is a square area with one side of 150 mm). The size of one side of the main surface 11 of the substrate is 151.2 mm, and the margin with respect to the design area is quite small.

Next, the light-transmitting substrate 10 on which the light-shielding film (CrOC film) 30 was formed was subjected to heat treatment. Specifically, heat treatment was performed using a hot plate at a heating temperature of 280° C. and a heating time of 5 minutes in the atmosphere. After the heat treatment, the ArF of the layered structure of the phase shift film 20 and the light shielding film 30 is measured using a spectrophotometer (Cary 4000 manufactured by Agilent Technologies) on the transparent substrate 10 on which the phase shift film 20 and the light shielding film 30 are laminated. When the optical density was measured at the wavelength of excimer laser light (approximately 193 nm), it was confirmed that it exceeded 2.0.

Next, enlarged image data was obtained using a CCD camera for each of the four corners of the main surface 11a of the light-transmitting substrate 10 on which the light-shielding film 30 was formed. In each of the acquired image data, the boundary between the light shielding film 30 and the main surface 11a could be visually recognized. However, in the image data of each of the four corners, a location was found where the main surface 11a was completely covered with the light shielding film 30 (the light shielding film 30 may have wrapped around the chamfered surface 13). . In other words, it was found that the masking plate could not be placed at an appropriate position. Therefore, for each of the image data at the four corners, using the side surface 12 as a reference, the area where the main surface 11a is exposed (the area where the light shielding film 30 is not formed) and the area where the light shielding film 30 is formed are determined. The distance to each boundary was measured. From this result, the difference between the center 17 of the transparent substrate 10 and the center of the masking plate during sputtering was calculated, and the installation position of the masking plate was finely adjusted.

Next, another transparent substrate 10 was prepared, and a phase shift film 20 and a light shielding film 30 were formed by sputtering in the same manner as above. Further, image data of each of the four corners of the main surface 11a of the light-transmitting substrate 10 on which the light-shielding film 30 was formed was obtained using the same procedure as above. Then, using the same procedure as above, for each of the image data at the four corners, calculate the distance to the boundary between the area where the main surface 11a is exposed and the area where the light shielding film 30 is formed, using the side surface 12 as a reference. were measured respectively. As a result, the boundary between the area where the main surface 11a is exposed and the area where the light shielding film 30 is formed was visible at all four corners. Moreover, the distance to the boundary with respect to the side surface 12 was also approximately the same.

Next, the film thickness profile near the boundary between the main surface 11a and the light-shielding film 30 was measured using a contact type micro-shape measuring machine (ET-4000 manufactured by Kosaka Institute). The results are shown in FIG. From this result, it was found that the light shielding film 30 began to be formed at a distance between 0.47 mm and 0.53 mm toward the inner side from the side surface 12 on the main surface 11a. In addition, from the above image data, the surface reflectance Rf for light with a wavelength of 400 nm to 700 nm was measured at multiple measurement points (locations) where the thickness of the light shielding film 30 was between 9 nm and 10 nm, and the average was 23.65%. The surface reflectance Rf for light within the above wavelength range was 20% or more in all cases. Furthermore, when the contrast ratio (Rf/Rs) of the surface reflectance Rf of the light-shielding film 30 at the above measurement location to the surface reflectance Rs of the main surface 11a was calculated, the minimum value was 3.29, which was 3.0 or more. It became. Furthermore, at the measurement location where the surface reflectance Rf is maximum (24.69%), the surface reflectance RfB for light with a wavelength of 400 nm is 24.96%, and the surface reflectance RfG for light with a wavelength of 550 nm is 25.06%. , the surface reflectance RfR for light with a wavelength of 700 nm was 24.08%. The standard deviation calculated between the three surface reflectances RfB, RfG, and RfR was 0.441, which was 1.0 or less.

The area in which the light shielding film 30 is formed (i.e., the inner region 14) is divided into areas of 55 μm x 55 μm, and the average film thickness of the light shielding film 30 is determined by taking the average of the film thicknesses measured in each area. Calculated. The calculated average thickness of the light shielding film 30 was 18 nm.

Next, another transparent substrate 10 was prepared, and the phase shift film 20 was formed by sputtering in the same manner as above, and the light shielding film 30 was formed by sputtering at the finely adjusted masking plate installation position. Next, the transparent substrate 10 on which the phase shift film 20 and the light shielding film 30 are laminated is placed in a single-wafer type DC sputtering apparatus, and a silicon (Si) target is used, and argon (Ar) and nitrogen monoxide (nitrogen monoxide) are used. A hard mask film 31 made of silicon, nitrogen, and oxygen is formed with a thickness of 5 nm on the light shielding film 30 and inside the edges of the light shielding film 30 by reactive sputtering (DC sputtering) in a mixed gas atmosphere of NO). It was formed by At this time, a masking plate having a square opening of 146 mm on one side with respect to the center of the substrate was used. Further, a predetermined cleaning treatment was performed to produce the mask blank 100 of Example 1.

A light-shielding film 30 alone was formed on the main surface 11a of another light-transmitting substrate 10 under the same conditions, and a heat treatment was performed. When the sheet resistance value of the light shielding film 30 was measured, it was 0.246 kΩ/Square, which was less than 0.5 kΩ/Square. Further, using a spectroscopic ellipsometer, the refractive index n and extinction coefficient k of the light shielding film 30 for light with a wavelength of 400 nm to 700 nm were measured. As a result, the extinction coefficient k for light with a wavelength of 400 nm is 2.33, the extinction coefficient k for light with a wavelength of 550 nm is 2.53, and the extinction coefficient k for light with a wavelength of 700 nm is 3.01. The above was confirmed. The refractive index n for light with a wavelength of 400 nm was 2.52, the refractive index n for light with a wavelength of 550 nm was 2.96, and the refractive index n for light with a wavelength of 700 nm was 3.57.

Further, the light shielding film 30 was analyzed by X-ray photoelectron spectroscopy (XPS, with RBS correction). As a result, the region near the surface of the light-shielding film 30 on the side opposite to the transparent substrate 10 (region up to a depth of about 2 nm from the surface) has a composition gradient ( It was confirmed that the oxygen content was 40 atomic % or more. Further, it was found that the average content of each constituent element in the region of the light shielding film 30 excluding the compositionally inclined portion was 71 atomic % for Cr, 14 atomic % for O, and 15 atomic % for C. Furthermore, the difference in each constituent element in the thickness direction of the region of the light-shielding film 30 excluding the compositionally gradient portion was 3 atomic % or less, and it was confirmed that there was substantially no compositionally gradient in the thickness direction.

Next, using the mask blank 100 of Example 1, a halftone phase shift mask 200 of Example 1 was manufactured in the following procedure. First, the surface of the hard mask film 31 was subjected to HMDS treatment. Subsequently, a resist film made of a chemically amplified resist for electron beam writing was formed to a thickness of 80 nm in contact with the surface of the hard mask film 31 by a spin coating method. Next, a first pattern, which is a phase shift pattern to be formed on the phase shift film 20, is drawn with an electron beam on this resist film, and predetermined development processing and cleaning processing are performed to form a resist having the first pattern. A pattern 40a was formed (see FIG. 3(a)). During this electron beam lithography, the light shielding film 30 was brought into contact with an earth pin (not shown) at the earth pin grounding location 16. As a result, the electron beam was drawn at a desired position on the resist film, and a desired resist pattern 40a could be formed.

Next, using the resist pattern 40a as a mask, dry etching was performed using CF ₄ gas to form a hard mask pattern 31a, which is a first pattern, on the hard mask film 31 (see FIG. 3(b)).

Next, the resist pattern 40a was removed. Next, using the hard mask pattern 31a as a mask, dry etching is performed using a mixed gas of chlorine gas (Cl ₂ ) and oxygen gas (O ₂ ) (gas flow rate ratio Cl ₂ :O ₂ =13:1). A light-shielding pattern 30a, which is pattern No. 1, was formed on the light-shielding film 30 (see FIG. 3(c)).
Next, using the light shielding pattern 30a as a mask, dry etching is performed using fluorine-based gas (SF ₆ +He) to form a phase shift pattern 20a, which is a first pattern, on the phase shift film 20, and at the same time, a hard mask pattern is formed. 31a was removed (see FIG. 3(d)).

Next, a resist film made of a chemically amplified resist for electron beam drawing was formed to a thickness of 150 nm on the light shielding pattern 30a by spin coating. Next, a second pattern, which is a pattern to be formed on the light-shielding film (a pattern including a light-shielding band pattern), is exposed and drawn on the resist film, and a predetermined process such as development is further performed to form a light-shielding pattern. A resist pattern 40b was formed (see FIG. 3(e)). Next, using the resist pattern 40b as a mask, dry etching is performed using a mixed gas of chlorine gas (Cl ₂ ) and oxygen gas (O ₂ ) (gas flow rate ratio Cl ₂ :O ₂ =4:1). A light-shielding pattern 30b having the pattern shown in FIG. 3 was formed on the light-shielding film 30 (see FIG. 3(f)). Further, the resist pattern 40b was removed and a predetermined process such as cleaning was performed to obtain a phase shift mask 200 (see FIG. 3(g)).

A simulation of a transferred image when the phase shift mask 200 produced through the above procedure is exposed and transferred onto a resist film on a semiconductor device using exposure light with a wavelength of 193 nm using AIMS193 (manufactured by Carl Zeiss) was performed. went. When the exposed transfer image of this simulation was verified, it fully met the design specifications. From this result, even if the phase shift mask 200 of Example 1 is set on the mask stage of an exposure device and exposed and transferred to a resist film on a semiconductor device, the circuit pattern ultimately formed on the semiconductor device will be It can be said that it can be formed with precision.

(Comparative example 1)
[Manufacture of mask blank]
The mask blank of Comparative Example 1 was manufactured in the same manner as in Example 1 except for the light shielding film. The light shielding film of Comparative Example 1 has different film forming conditions from the light shielding film 3 of Example 1. Specifically, a light-transmitting substrate on which a phase shift film was formed was installed in a single-wafer type DC sputtering apparatus, and a chromium (Cr) target was used to sputter argon (Ar), carbon dioxide (CO ₂ ), and helium. Reactive sputtering (DC sputtering) was performed in a mixed gas atmosphere of (He). As a result, a light-shielding film (CrOC film) made of chromium, oxygen, and carbon was formed with a thickness of 24 nm in contact with the phase shift film. It should be noted that during sputtering to form this light-shielding film 30, a masking plate having a square opening with each side of 150 mm was used as in Example 1.

Next, the light-transmitting substrate on which the light-shielding film (CrOC film) was formed was subjected to heat treatment under the same conditions as in Example 1. After the heat treatment, the light from the ArF excimer laser with the layered structure of the phase shift film and the light shielding film was measured using a spectrophotometer (Cary 4000 manufactured by Agilent Technologies) on the transparent substrate on which the phase shift film and the light shielding film were laminated. When the optical density at a wavelength (approximately 193 nm) was measured, it was confirmed that it was 3.0 or more.

Next, in the same procedure as in Example 1, enlarged image data was obtained using a CCD camera for each of the four corners of the main surface of the light-transmitting substrate on which the light-shielding film of Comparative Example 1 was formed. However, in each of the acquired image data, it was difficult to visually recognize the boundary between the light shielding film and the main surface. For this reason, it has been difficult to calculate the difference between the center 17 of the transparent substrate 10 and the center of the masking plate during sputtering and to finely adjust the installation position of the masking plate with high precision.

Next, the film thickness profile near the boundary between the main surface and the light-shielding film of Comparative Example 1 was measured using a contact micro-shape measuring device (ET-4000 manufactured by Kosaka Institute). From the above image data, we measured the surface reflectance Rf for light with a wavelength of 400 nm to 700 nm at multiple measurement points (points) where the thickness of this light shielding film was between 9 nm and 10 nm, and found that the average was 14.85%. , the surface reflectance Rf for light within the above wavelength range was significantly less than 20%. Furthermore, when the contrast ratio (Rf/Rs) of the surface reflectance Rf of the light-shielding film of Comparative Example 1 at the above measurement location with respect to the surface reflectance Rs of the main surface was calculated, the maximum was 2.27, and 3. It was significantly below 0. Furthermore, the surface reflectance RfB for light with a wavelength of 400 nm at the measurement point where the surface reflectance Rf is maximum (15.51%) is 17.85%, and the surface reflectance RfG for light with a wavelength of 550 nm is 15.37%. , the surface reflectance RfR for light with a wavelength of 700 nm was 13.32%. The standard deviation calculated between the three surface reflectances RfB, RfG, and RfR was 1.853, which was significantly greater than 1.0.

In addition, by dividing the area where this light shielding film 30 is formed (that is, the inner region 14) into areas of 55 μm x 55 μm and taking the average of the film thicknesses measured in each area, the average thickness of the light shielding film 30 is calculated. The thickness was calculated. The calculated average thickness of the light shielding film 30 was 24 nm.

A light-shielding film alone was formed on the main surface of another light-transmitting substrate under the same conditions, and a heat treatment was performed. When the sheet resistance value of the light shielding film of Comparative Example 1 was measured, it was 168 kΩ/square, which was significantly higher than 1.0 kΩ/square. Furthermore, using a spectroscopic ellipsometer, the refractive index n and extinction coefficient k of the light-shielding film with respect to light having a wavelength of 400 nm to 700 nm were measured. As a result, the extinction coefficient k for light with a wavelength of 400 nm is 1.23, the extinction coefficient k for light with a wavelength of 550 nm is 1.27, the extinction coefficient k for light with a wavelength of 700 nm is 1.2, and 2.0. It was below. The refractive index n for light with a wavelength of 400 nm was 2.42, the refractive index n for light with a wavelength of 550 nm was 2.64, and the refractive index n for light with a wavelength of 700 nm was 2.67.

Furthermore, the light shielding film was analyzed by X-ray photoelectron spectroscopy (XPS, with RBS correction). As a result, a region near the surface of the light-shielding film on the side opposite to the light-transmitting substrate (a region up to a depth of approximately 2 nm from the surface) has a composition gradient region (oxygen-containing It was confirmed that the amount was 40 atomic % or more. It was also found that the average content of each constituent element in the region of the light-shielding film excluding the compositional gradient portion was 56 at. % for Cr, 29 at. % for O, and 15 at. % for C. Further, the difference in each constituent element in the thickness direction of the region of the light-shielding film excluding the compositionally gradient portion was all 3 atomic % or less, and it was confirmed that there was substantially no compositionally gradient in the thickness direction.
With the light-shielding film in Comparative Example 1, it was difficult to visually recognize the boundary between the area where the main surface was exposed and the area where the light-shielding film was formed, so the masking plate installation position was finely adjusted with high precision. It was difficult to do. For this reason, it is difficult to reliably prevent the light-shielding film from being formed around the side surface or chamfered surface of the substrate.

[Manufacture of phase shift mask]
Next, using this mask blank of Comparative Example 1, a plurality of phase shift masks of Comparative Example 1 were produced in the same manner as in Example 1.

The phase shift mask of Comparative Example 1 was exposed and transferred onto a resist film on a semiconductor device using exposure light with a wavelength of 193 nm using AIMS193 (manufactured by Carl Zeiss) in the same manner as in Example 1. A simulation was performed. When the exposed transfer images of this simulation were verified, transfer defects were confirmed in some phase shift masks. This is thought to be due to the inability to accurately draw a pattern due to charge-up of the resist, and the generation of dust due to adhesion of the light-shielding film to the chamfered surface of the substrate, which are considered to be the causes of the transfer failure. From this result, when the phase shift mask of Comparative Example 1 is set on the mask stage of an exposure device and exposed and transferred to a resist film on a semiconductor device, defective areas will be found in the circuit pattern finally formed on the semiconductor device. It can be said that this will occur.

10 Transparent substrate 11 (11a, 11b) Main surface 12 Side surface 13 Chamfered surface 14 Inner region 15 Outer region 16 Earth pin grounding point 17 Center 20 Phase shift film 20a Phase shift pattern 30 Light shielding film 30a, 30b Light shielding pattern 31 Hard mask film 31a Hard mask patterns 40a, 40b Resist pattern 50 Sputtering target 51 Substrate holder 52 Shield plate 100 Mask blank 200 Phase shift mask

Claims (10)

A mask blank comprising a substrate and a thin film,
The substrate has two main surfaces and a side surface, and a chamfered surface is provided between the two main surfaces and the side surface,
One of the two main surfaces has an inner region including the center of the main surface and an outer peripheral region outside the inner region,
the thin film is provided on an inner region of the main surface;
The surface reflectance Rs of the outer peripheral region of the main surface with respect to light with a wavelength of 400 nm to 700 nm is 10% or less,
When the surface reflectance for light with a wavelength of 400 nm to 700 nm at one of the locations where the film thickness of the thin film is within the range of 9 nm to 10 nm is Rf, the contrast ratio (Rf/Rs) is 3.0. A mask blank characterized by the above. 2. The mask blank according to claim 1, wherein the surface reflectance at the one location is 20% or more for light having a wavelength of 400 nm to 700 nm. When the surface reflectance for light with a wavelength of 400 nm at the one location is RfB, the surface reflectance for light with a wavelength of 550 nm at the one location is RfG, and the surface reflectance for light with a wavelength of 700 nm at the one location is RfR. The mask blank according to claim 1 or 2, wherein a standard deviation calculated between the three surface reflectances RfB, RfG, and RfR is 1.0 or less. 4. The mask blank according to claim 1, wherein the thin film has an extinction coefficient k of 1.5 or more for light having a wavelength of 400 nm to 700 nm. 5. The mask blank according to claim 1, wherein the thin film has an average thickness of greater than 10 nm and less than or equal to 60 nm. 6. An intermediate film is provided between the main surface and the thin film in the inner region from the outer edge of the inner region toward the center of the one main surface. Mask blank described in any of the above. 7. The mask blank according to claim 6, wherein the intermediate film is a semi-transparent film that transmits exposure light from an ArF excimer laser with a transmittance of 1% or more. A transfer mask, characterized in that the thin film of the mask blank according to claim 1 is provided with a transfer pattern. 8. A transfer mask according to claim 6, wherein the intermediate film in the mask blank has a transfer pattern, and the thin film has a pattern including a light-shielding band. A method for manufacturing a semiconductor device, comprising the step of exposing and transferring a transfer pattern onto a resist film on a semiconductor substrate using the transfer mask according to claim 8 or 9.

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